Weird Apollo server error-could not connect to endpoint

[Karem1986]

I have defined my schema for query Messages, resolver and mutation, also the subscription. Followed the docs for Apollo server subscription but it keeps giving the same error.
I tried to use the Subscribe server from the docs but nothing works
please see here the code and further explanation of this apollo server subscriptions issue:

https://stackoverflow.com/questions/65642947/weird-apollo-server-error-could-not-connect-to-endpoint